Ideas
Sims die of broken heart too easily and there's no way to cure a broken heart.
Every unsuccessful romantic interaction increases commodity_Death_BrokenHeart which causes the death by broken heart when the value exceeds 95. However, there's no way to decrease that value. Successful romantic interactions make the broken heart moodlets disappear faster but the actual commodity remains unchanged. That means even without a broken heart moodlet, one unsuccessful romantic interaction may be enough to kill your sim without a warning.
A solution would be to reset the commodity when the moodlet expires, so that there wouldn't be surprise deaths.
Successful interactions kill you just the same. Playing a character who has zero unsuccessful interaction. And keeps dying after every woohoo, no matter with whom (she did a lot of them I admit).